Which of the following options is incorrect?

Options

A. A regular pentagon has only five lines of symmetry.
B. A square has four lines of symmetry.
C. A pentagonal prism has 10 edges.
D. A tetrahedron has 4 faces.

Answer

To solve the question, we need to evaluate the given options regarding their correctness. Let's analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding the Options**:
- The first option states that a regular pentagon has only 5 lines of symmetry.
- The second option states that a square has 4 lines of symmetry.
- The third option states that a pentagonal prism has only 10 edges.

2. **Evaluating the First Option**:
- A regular pentagon has 5 equal sides and 5 equal angles.
- The lines of symmetry in a regular pentagon can be drawn from each vertex to the midpoint of the opposite side.
- Therefore, there are indeed **5 lines of symmetry** in a regular pentagon.
- **Conclusion**: The first option is correct.

3. **Evaluating the Second Option**:
- A square has 4 equal sides and 4 equal angles.
- The lines of symmetry in a square can be drawn:
- 2 diagonals
- 2 lines that bisect the sides (one vertical and one horizontal)
- Thus, a square has **4 lines of symmetry**.
- **Conclusion**: The second option is correct.

4. **Evaluating the Third Option**:
- A pentagonal prism has two pentagonal bases and rectangular sides.
- To find the number of edges:
- Each pentagonal base has 5 edges.
- There are 5 additional edges connecting the corresponding vertices of the two bases.
- Therefore, the total number of edges is:
- 5 (from the top base) + 5 (from the bottom base) + 5 (connecting edges) = **15 edges**.
- **Conclusion**: The third option is incorrect as it states there are only 10 edges.

5. **Final Answer**:
- The incorrect option is **Option 3**.